The UTM Grid System

All GPS receivers can provide position information in terms of latitude, longitude, and height, and usually in a variety of selectable geodetic datums. For many purposes, position information in this format is more than adequate. However, when plotting position information on maps or carrying out supplemental calculations using the position coordinates, it can be advantageous to work instead with the corresponding grid coordinates on a particular map projection. One of the most widely used map projection and grid systems is the Universal Transverse Mercator (UTM) system. Many GPS receivers can directly output position information in UTM coordinates. In this month’s column, we’ll take a look at the UTM system, see how UTM grid coordinates are related to geodetic coordinates, and indicate the corrections to be applied to grid distances and bearings to get the actual true quantities on the earth’s surface. “Innovation” is a regular column featuring discussions about recent advances in GPS technology and its applications as well as the fundamentals of GPS positioning. The column is coordinated by Richard B. Langley of the Department of Geodesy and Geomatics Engineering at the University of New Brunswick, who appreciates receiving your comments as well as topic suggestions for future columns. To contact him, see the “Columnists” section on page 4 of this issue.